The invention relates to a composite constructional element which comprises in particular a basic body consisting of thermoplastic material and a reinforcing element which can be connected to said basic body, said element being used for example in the automotive industry.
DE-1950 139 relates to an impeller made of plastic. This comprises a hub and blades extending from the latter, the hub being made up of two concentric rings, if appropriate forming an integral part. Cast into the interior is a metal base, which has the form of a cup and is provided in its upright edge with holes through which the polymer melt flows during the injection-molding process. For producing impellers it is possible to use various hub bases, which have shaft bores of various sizes and/or different numbers of holes for the fastening screws, with hole circles of a wide variety of diameters being possible as well as various cup heights, allowing the distance from the clamping plane to the front edge of the blades to be changed.
DE-1956 826 concerns a lightweight plastic beam, in which a reinforced corrugated plastic plate is laminated in a U-shaped upper flange profile and a U-shaped lower flange profile, consisting of reinforced plastic. For absorbing the greatest structural stresses, prestressing reinforcements may be respectively laminated into the flange profiles.
EP-0 370 342 B1 discloses a lightweight constructional element. The lightweight constructional element comprises a shell-shaped basic body, the interior of which has reinforcing ribs. These are permanently connected to the basic body. The reinforcing ribs consist of molded-on plastic, the connection of which to the basic body is effected at discrete connection points by openings in the basic body through which the plastic flows during the injection-molding process. The anchoring means forming the discrete connection points are formed as beads. The basic body of the lightweight constructional element may at least partially have a coating layer which consists of the same material as the reinforcing ribs.
To improve the connection between the reinforcing ribs and the basic body, deformations are provided at the edges of the openings. The reinforcing ribs have at the connection points with the basic body a widened foot region, to achieve improved force introduction. The free spaces formed between the reinforcing ribs on the lightweight constructional element according to EP-0 37 342 B1 have essentially a trapezoidal cross section.
In the case of structures made up of lightweight constructional elements produced in this way and connected to one another, the reinforcing ribs are molded onto the basic body by injection molding and form with the latter a composite constructional element; the reinforcing ribs consisting of plastic and the shell-shaped basic body produced from metal may have different expansion characteristics when subjected to temperature changes, it being possible for this to cause the undesired build-up of stresses at the connection points in the region of the openings on the shell-shaped basic body and on the reinforcing ribs. Since the molding of reinforcing ribs of plastic onto the shell-shaped basic body necessitates very closely toleranced add-on parts for inserting into the open injection mold and requires the simultaneous handling of the metal constructional element and the plastic to be molded on, complex handling mimics and time-consuming operations for positioning the basic bodies in the injection mold are required. This may result in longer cycle times and, seen overall, more expensive production of the constructional elements.
In view of the prior-art solutions presented, it is an object of the present invention to avoid the disadvantages mentioned above and permit more cost-effective production of composite constructional elements with improved longitudinal expansion characteristics.
This object is achieved according to the invention in a process for producing a composite constructional element from a basic body made of plastic which is provided with ribs and is partially or completely connected to a reinforcing element made of metal or reinforced plastic by the connection of the basic body and reinforcing element to form a composite constructional element for the transfer of shearing, torsional, flexural and tensile/compressive stresses taking place at a subsequent time.
The separation, proposed according to the invention, of the simultaneous production and concomitant connection of the basic body and reinforcing element allows the composite constructional element to be produced considerably more easily and cost-effectively. The subsequently occurring operation of connecting two components of different materials makes it possible to produce each component under optimum conditions, so that complexities arising in the simultaneous handling of constructional elements and materials of different properties, and consequently more complex handling, can be avoided.
In a further refinement of the idea underlying the invention, a subsequent connection of the basic body and reinforcing element can be created by means of a material bond. In this way, the inner side of the reinforcing element and the outer side of the basic body can be welded or adhesively bonded to one another either over their full surface area or only partially. Applying a layer of adhesive between the two constructional elements to be connected to one another allows a further layer of material to be created, which for example absorbs shearing stresses and considerably improves the mechanical properties of the composite constructional element.
In addition to the possibility of connecting the basic body and the reinforcing element to one another by a material bond, these two constructional elements can also be connected to one another by a form fit after their production, taking place separately in each case. In this way, openings can be provided on the reinforcing element, which may preferably consist of metal or else reinforced plastic, said openings being capable of being created by cold forming, by the effect of heat or else by vibration, lending the openings an approximately funnel-shaped appearance. When the basic body is pressed together with the reinforcing element, the funnel-shaped regions of the reinforcing element penetrate into the softened thermoplastic of the basic body under the effect of heat or vibration and form a rivet-like connection.
To create a form-fitting connection between the basic body and the reinforcing element essentially sheathing the latter, anchoring attachments into which fastening elements engage, such as for example self-tapping or thread-forming screws, can be molded onto the basic body. A form-fitting connection between the ribbed basic body and the reinforcing element can also be created by rivet pins made of plastic being formed on the basic body, produced by the injection-molding technique, in that, after connecting the basic body and the reinforcing element, the end regions of the rivets passing through the openings on the reinforcing element are re-shaped in a separate operation. A form-fitting connection created in this way between the basic body and the reinforcing element still allows relative movement between the basic body and the reinforcing element when there are longitudinal expansions of the composite constructional element, so that there is no build-up of internal stresses, exerting a load on the constructional element, when it is subjected to temperature changes.
The form-fitting connection on the basic body and on the reinforcing element can be achieved by, for example, butt straps fashioned on the reinforcing element in a certain length being bent around the basic body enclosed for the most part by the reinforcing element. This allows compensation for stresses caused by longitudinal expansion to be brought about in a simple way by a sliding movement, since the relative movement between the two constructional elements is possible without any problems, without significantly impairing the strength of the constructional element.
To achieve a form-fitting connection between the basic body and the reinforcing element, snap elements may also be provided on the basic body, engaging in openings on the reinforcing element or on the basic body which are dimensioned in such a way that it is possible to compensate for thermally induced stresses in a simple way by relative movement at the connection points between the two constructional elements.
A composite constructional element produced according to the variants of the process described above can be produced significantly more cost-effectively, since there is no intervention in the production processes for the individual constructional elements and the joining together of the basic body and reinforcing element only takes place at a subsequent time.